Method, Apparatus, and System for Service Control Via I1 Interface

ABSTRACT

Embodiments of the present invention disclose a method, an apparatus, and a system for service control via an I1 interface. The method includes: sending a Session Initiation Protocol Invite message to a user equipment through a Gm interface; if receiving a response message returned by the user equipment, where the response message indicates that the user equipment chooses to use a circuit switched bearer and use an I1 interface for control, sending an I1 Invite message to the user equipment through the I1 interface, where I1 Invite message carries information indicating that Gm interface control falls back to the I1 interface control and information used to associate the Session Initiation Protocol Invite message.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of international Application No.PCT/CN2010/075724, filed on Aug. 5, 2010, which claims priority toChinese Patent Application No. 200910165624.8, filed on Aug. 12, 2009,both of which are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to the field of communicationtechnologies, and in particular, to a method, an apparatus, and a systemfor service control via the I1 interface.

BACKGROUND OF THE INVENTION

IMS centralized services (IMS Centralized Services, ICS) support use ofcircuit switched (Circuit Switched, CS) access to bear a media stream toimplement Internet Protocol multimedia subsystem (IP MultimediaSubsystem, IMS) services. A service centralization and continuity(Service Centralization and Continuity, SCC) application server(Application Server, AS) is an application server that supports the ICSand is used to act as an agent of a user equipment (User Equipment, UE)to perform IMS session control, for example, being triggered by the UEto initiate an IMS session.

The ICS working group already completes the standardization of theframework, and implementation of the standardization of the ongoingprotocol relates to stipulating a new protocol, that is, an ICS controlprotocol (or known as an I1 protocol). The I1 protocol is an applicationprotocol on the I1 interface. The I1 interface is a new interfaceintroduced by the ICS working group. The I1 interface is located betweenthe UE and the SCC AS and used to transfer IMS service controlsignaling. The I1 interface is based on CS access, for example, theapplication protocol message of the I1 interface is transferred throughunstructured supplementary service data (Unstructured SupplementaryService Data, USSD) or short message service (Short Message Service,SMS).

Considering the SCC AS in the ICS needs to implement an interworkingoperation between the I1 protocol and the Session Initiation Protocol(Session Initiation Protocol, SIP), the I1 protocol may use most ofconcepts or terms of the SIP. To make a difference, an I1 prefix isusually added before the concepts or terms of SIP to indicate theconcepts or terms of the I1 protocol.

Because there are a large number of IMS sessions, the I1 protocol, as anIMS session control protocol, also has a large traffic volume (that is,overheads generated in the transfer of I1 protocol messages). Variousapplications or value-added services are already developed on the basisof the USSD or the SMS. Therefore, if the I1 protocol uses the USSD orthe SMS as the transmission protocol, traffic of the USSD or the SMS maybe greatly affected. Therefore, the ICS working group requires that themessage overheads of the I1 protocol should be minimized during thedesign.

SUMMARY OF THE INVENTION

The technical problem to be solved by embodiments of the presentinvention is to provide a method, an apparatus, and a system for servicecontrol via the I1 interface.

To solve the above technical problem, the method for service control viathe I1 interface according to the present invention may be implementedby using the following technical solution:

sending a Session Initiation Protocol Invite message to a user equipmentthrough a Gm interface; and

if receiving a response message returned by the user equipment, wherethe response message indicates that the user equipment chooses to use acircuit switched bearer and an I1 interface for control,

sending an I1 Invite message to the user equipment through the I1interface, where the I1 Invite message carries information indicatingthat Gm interface control falls back to the I1 interface control andinformation used to associate the Session Initiation Protocol Invitemessage.

An embodiment of the present invention also provides a method forservice control via the I1 interface, including:

receiving an I1 Invite message sent by a user equipment, where the I1Invite message carries a service control switching request indicationand a Session Initiation Protocol dialog identifier of an InternetProtocol multimedia subsystem session;

searching for the Internet Protocol multimedia subsystem session throughthe Session Initiation Protocol dialog identifier; and

sending a message, which indicates that service control is switchedsuccessfully, to the user equipment.

An embodiment of the present invention also provides a servicecentralization and continuity application server, including:

a Session Initiation Protocol Invite message sending unit, configured tosend a Session Initiation Protocol Invite message to a user equipmentthrough a Gm interface;

a response message receiving unit, configured to receive a responsemessage returned by the user equipment, where the response messageindicates that the user equipment chooses to use a circuit switchedbearer and use an I1 interface for control; and

an I1 Invite message sending unit, configured to send an I1 Invitemessage to the user equipment through the I1 interface if the responsemessage receiving unit receives the response message, where the I1Invite message carries information indicating that Gm interface controlfalls back to the I1 interface control and information used to associatethe Session Initiation Protocol Invite message.

An embodiment of the present invention also provides an servicecentralization and continuity application server, including:

an I1 Invite message receiving unit, configured to receive an I1 Invitemessage sent by a user equipment, where the I1 Invite message carries aservice control switching request indication and a Session InitiationProtocol dialog identifier of an Internet Protocol multimedia subsystemsession;

a session searching unit, configured to search for the Internet Protocolmultimedia subsystem session through the Session Initiation Protocoldialog identifier; and

a switching success message sending unit, configured to send a message,which indicates that service control is switched successfully, to theuser equipment.

An embodiment of the present invention also provides a user equipment,including:

an Invite message receiving unit, configured to receive, through a Gminterface, a Session Initiation Protocol Invite message sent by aservice centralization and continuity application server;

a response message sending unit, configured to send a response messageafter the Session Initiation Protocol Invite message is received, wherethe response message indicates that the user equipment chooses to use acircuit switched bearer and use an I1 interface for control;

an I1 Invite message receiving unit, configured to receive an I1 Invitemessage through the I1 interface; and

an I1 Invite message parsing unit, configured to: parse the I1 Invitemessage to obtain information indicating that Gm interface control fallsback to the I1 interface control and information used to associate theSession Initiation Protocol Invite message.

An embodiment of the present invention also provides a user equipment,including:

an I1 Invite message sending unit, configured to send an I1 Invitemessage to an service centralization and continuity application server,where the I1 Invite message carries a service control switching requestindication and a Session Initiation Protocol dialog identifier of anInternet Protocol multimedia subsystem session; and

a switching success message receiving unit, configured to receive amessage indicating that service control is switched successfully.

An embodiment of the present invention also provides a system forservice control via the I1 interface, including:

a service centralization and continuity application server and a userequipment.

The service centralization and continuity application server includes:

a Session Initiation Protocol Invite message sending unit, configured tosend a Session Initiation Protocol Invite message to the user equipmentthrough a Gm interface;

a response message receiving unit, configured to receive a responsemessage returned by the user equipment, where the response messageindicates that the user equipment chooses to use a circuit switchedbearer and use an I1 interface for control; and

an I1 Invite message sending unit, configured to send an I1 Invitemessage to the user equipment through the I1 interface if the responsemessage receiving unit receives the response message, where the I1Invite message carries information indicating that Gm interface controlfalls back to the I1 interface control and information used to associatethe Session Initiation Protocol Invite message.

The user equipment includes:

an Invite message receiving unit, configured to receive, through a Gminterface, a Session Initiation Protocol Invite message sent by theservice centralization and continuity application server;

a response message sending unit, configured to send a response messageafter the Session Initiation Protocol Invite message is received, wherethe response message indicates that the user equipment chooses to use acircuit switched bearer and use an I1 interface for control;

an I1 Invite message receiving unit, configured to receive an I1 Invitemessage through the I1 interface; and

an I1 Invite message parsing unit, configured to: parse the I1 Invitemessage to obtain information indicating that Gm interface control fallsback to the I1 interface control and information used to associate theSession Initiation Protocol Invite message.

An embodiment of the present invention provides another system forservice control via the I1 interface, including:

a service centralization and continuity application server and a userequipment.

The service centralization and continuity application server includes:

an I1 Invite message receiving unit, configured to receive an I1 Invitemessage sent by the user equipment, where the I1 Invite message carriesa service control switching request indication and a Session InitiationProtocol dialog identifier of an Internet Protocol multimedia subsystemsession;

a session searching unit, configured to search for the Internet Protocolmultimedia subsystem session through the Session Initiation Protocoldialog identifier; and

a switching success message sending unit, configured to send a message,which indicates that service control is switched successfully, to theuser equipment.

The user equipment includes:

an I1 Invite message sending unit, configured to send an I1 Invitemessage to the service centralization and continuity application server,where the I1 Invite message carries a service control switching requestindication and a Session Initiation Protocol dialog identifier of anInternet Protocol multimedia subsystem session; and

a switching success message receiving unit, configured to receive amessage indicating that service control is switched successfully.

The foregoing technical solution has the following benefits: A replaceheader field of the I1 Invite message is used to carry informationindicating that Gm interface control falls back to the I1 interfacecontrol and information used to associate the Session InitiationProtocol Invite message, which may omit the calling user identifier andthe called user identifier, and reduces overheads of the I1 protocolmessage.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate the technical solution in the embodiments of the presentinvention or in the prior art more clearly, the accompanying drawingsfor describing the embodiments of the present invention or the prior artare briefly described below. Evidently, the accompanying drawings areonly some embodiments of the present invention, and persons of ordinaryskill in the art can derive other drawings from these accompanyingdrawings without any creative effort.

FIG. 1 is a schematic flowchart of a method for an ICS UE to callaccording to an embodiment of the present invention;

FIG. 2 is a schematic flowchart of a method for an ICS UE to be calledaccording to an embodiment of the present invention;

FIG. 3 is a schematic flowchart of a Gm fallback method according toembodiment 1 of the present invention;

FIG. 4 is a schematic flowchart of a method for Gm switching accordingto embodiment 2 of the present invention;

FIG. 5 is a schematic flowchart of a method for adding an I1 interfaceaccording to embodiment 3 of the present invention;

FIG. 6 is a schematic structural diagram of a service centralization andcontinuity application server according to embodiment 4 of the presentinvention;

FIG. 7 is a schematic structural diagram of the service centralizationand continuity application server according to embodiment 4 of thepresent invention;

FIG. 8 is a schematic structural diagram of a service centralization andcontinuity application server according to embodiment 5 of the presentinvention;

FIG. 9 is a schematic structural diagram of a service centralization andcontinuity application server according to embodiment 6 of the presentinvention;

FIG. 10 is a schematic structural diagram of a user equipment accordingto embodiment 7 of the present invention;

FIG. 11 is a schematic structural diagram of a system for servicecontrol via the I1 interface according to embodiment 8 of the presentinvention;

FIG. 12 is a schematic structural diagram of a system for servicecontrol via the I1 interface according to embodiment 9 of the presentinvention;

FIG. 13 is a schematic structural diagram of a system for servicecontrol via the I1 interface according to embodiment 10 of the presentinvention;

FIG. 14 is a schematic structural diagram of a system for servicecontrol via the I1 interface according to embodiment 11 of the presentinvention;

FIG. 15 is a schematic structural diagram of a user equipment accordingto embodiment 12 of the present invention;

FIG. 16 is a schematic structural diagram of the user equipmentaccording to embodiment 12 of the present invention;

FIG. 17 is a schematic structural diagram of a user equipment accordingto embodiment 13 of the present invention; and

FIG. 18 is a schematic structural diagram of the user equipmentaccording to embodiment 13 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The technical solutions provided by the embodiments of the presentinvention are hereinafter described clearly and completely withreference to the accompanying drawings in the embodiments of the presentinvention. Apparently, the embodiments described below are only a partrather than all of the embodiments of the present invention. Based onthe embodiments of the present invention, all other embodiments thatpersons of ordinary skill in the art derive without making any creativeeffort, fall within the protection scope of the present invention.

During the design of the I1 protocol, message overheads may be reducedfrom the following two perspectives: reducing information transfer andefficiently encoding information to be transferred. In the embodimentsof the present invention, the message overheads are reduced from theperspective of reducing information transfer.

The overhead optimization designs in the I1 protocol solution in callingand called scenarios are as follows:

(1) The I1 protocol does not include the via (Via) header function,record-route (Record-route) header function, and route (Route) headerfunction in SIP.

(2) As for the Session Description Protocol (Session DescriptionProtocol, SDP) functions, The I1 protocol includes only some of the, SDPfunctions in SIP.

(3) The I1 Invite (Invite) message includes the calling user identifierand the called user identifier of an IMS session. Subsequent responsesor requests do not need to include the calling user identifier and thecalled user identifier but use a combination of the Call-ID (Call-ID),From tag (From tag), and To tag (To tag) to associate the IMS session.

The following describes optimization solutions in the calling and calledscenarios:

Scenario 1: ICS UE is Calling

In this procedure, ICS UE A initiates an IMS session through the I1interface; the SCC AS allocates a public service identity directorynumber (Public Service Identity Directory Number, PSI DN) which is usedby the UE to initiate a CS call to establish a CS bearer (bearer) (theCS bearer is used to transmit media streams of the IMS session); afterthe SCC AS receives a SIP Invite (invite) message sent by the mobileswitching centre (Mobile Switching Centre, MSC) server (server) or themedia gateway control function (Media Gateway Control Function, MGCF) inthe CS domain, the SCC AS replaces UE A to generate a SIP Invite messageto initiate an IMS session. The specific procedure is as shown in FIG.1:

Step 101: ICS UE A sends an I1 Invite message through the I1 interfaceto initiate an IMS session, where the I1 Invite message includes thefollowing information:

an I1 Call-ID (Call-ID), used to identify the IMS session or call on theI1 interface, for example, set to 2037701kfjs;

an I1 From header (From header), where the value of the header field isused to indicate the calling user identifier of this session, forexample, set to user_a@example.com, where the From header also includesa tag (tag, where the tag is used to be combined with the I1 Call-ID toidentify the IMS session or Call on the I1 interface and the tag may notbe set or transferred to reduce the message overheads), for example, thetag is set to a2ci;

an I1 To header (To header), where the value of the header field is usedto indicate the called user identifier of the IMS session, for example,set to user_b@example.com; and

an I1 command sequence (CSeq, Command Sequence), used to indicate thesequence of the I1 command (or known as an I1 request or I1 method).When UE A generates the I1 Invite request, a numerical value is selectedat random as the CSeq value, for example, 1688. When UE A sends other I1requests subsequently, 1 is added to the CSeq value continuously. TheCSeq also includes method (method) information used to indicate an I1Invite message. The SCC AS may copy the CSeq when sending a response tothe I1 Invite message so that the UE A matches the I1 request with theI1 response. The I1 command may be the I1 Invite message or anothercommand (request or method) message sent through the I1 interface, andis not limited in the embodiment of the present invention.

Step 102: After receiving the I1 Invite message, the SCC AS stores theCall-ID, From header, To header, and command sequence (the SCC AS alsogenerates and maintains its own command sequence when sending an I1request subsequently), and sends an I1 session progress message, whichincludes the following information:

an I1 Call-ID, copied from the I1 Invite message;

an I1 From header, copied from the I1 Invite message, with the callinguser identifier being deleted;

an I1 To header, copied from the I1 Invite message, with the called useridentifier being deleted, where a tag (the tag is combined with the I1Call-ID to identify the IMS session or Call-ID on the I1 interface andmay not be set or transferred to reduce the message overhead) isgenerated and included in the To header, for example, tag=u7c3, wherethe I1 Call-ID, the I1 From tag, and the I1 To tag are combined touniquely identify an IMS session or a call on the I1 interface;

an I1 command sequence (CSeq), copied from the I1 Invite message; and

SDP (Session Description Protocol, Session Description Protocol)information, including a PSI DN used by ICS UE A to initiate a CS callto establish a CS bearer (or known as a CS connection), where the CSbearer is used to transmit media streams of the IMS session, and the PSIDN is associated with the SCC AS, for example, the PSI DN is set to+12125556666. The UE may subsequently send a CS call to the SCC AS byusing the PSI DN. In other I1 requests or responses, the SDP informationmay also include other information, for example, I1 Update (SDP(a=inactive)), which is used to indicate that the IMS session is held(hold).

Step 103 to step 104: ICS UE A initiates a CS call by using the PSI DNas a called number; the MSC server or the MGCF (Media Gateway ControlFunction, media gateway control function) in the CS domain performsconversion between CS signaling and SIP signaling, and generates a SIPInvite message (including the PSI DN), where the SIP Invite message isfinally transmitted to the SCC AS. The SCC AS associates the stored I1Invite message by using the PSI DN.

Note: After step 102, when UE A may send another I1 request, forexample, an I1 Update request, the CSeq:1689 Update should be set.

Step 105 to step 106: The SCC AS generates a SIP Invite message(including a called user identifier and CS bearer information, where theCS bearer information is used by UE B to transmit a media stream), wherethe SIP Invite message is finally transmitted to UE B. a user of UE Bpicks up the phone to accept the IMS session invitation, and sends asuccess message (200 OK) to indicate that the user already picks up thephone.

Step 107 to step 108: The SCC AS sends a 200 OK to the MSC server or theMGCF to indicate that the CS call is established successfully. The MSCserver sends a connect message to UE A to indicate that the CS call isestablished successfully.

Step 109: The SCC AS sends an I1 200 OK response through the I1interface to indicate that the IMS session is established successfully.The header field of the I1 200 OK is the same as that of an I1 sessionprogress message, while the SDP part does not include the PSI DN.

Step 110: The SCC AS sends a SIP ACK request to UE B to acknowledge the200 OK (received). The SCC AS does not need to wait for UE A toacknowledge the reception of the I1 200 OK, but may use reliabletransmission capability of the lower transport layer protocol (forexample, the USSD or the SMS).

Scenario 2: ICS UE is Called

In this procedure, the SCC AS delivers an IMS session Invite messagethrough the I1 interface, which includes a PSI DN used by the UE toinitiate a CS call to establish a CS bearer (used to transmit a mediastream of the IMS session). The specific procedure is as shown in FIG.2:

Step 201: The SCC AS receives a SIP Invite message that includes acalling user identifier (for example, set to user_b@example.com) and acalled user identifier (for example, set to user_a@example.com).

Step 202: The SCC AS sends an I1 Invite message to ICS UE A through theI1 interface, where the I1 Invite message includes the followinginformation (the information is also stored by the SCC AS):

an I1 Call-ID (Call-ID), used to identify the IMS session or call on theI1 interface, for example, set to 9t3j9xsdfw9tg374js7usjv;

an I1 From header (From header), used to indicate the calling useridentifier of the IMS session, for example, set to user_b@example.com,where the From header also includes a tag (tag), for example, the tag isset to kg48;

an I1 To header (To header), used to indicate the called user identifierof the IMS session, for example, set to user_b@example.com;

an I1 command sequence (CSeq, Command Sequence), for example, set toCSeq: 98 Invite; and

SDP (Session Description Protocol, Session Description Protocol)information, including a PSI DN used by the ICS UE A to initiate a CScall to establish a CS bearer (or known as a CS connection), forexample, the PSI DN is set to +12125558888.

Step 203: After receiving the I1 Invite message, ICS UE A stores the I1Call-ID, I1 From header, I1 To header, and I1 command sequence, andsends a I1 session progress message through the I1 interface, where theI1 session progress message includes the following information:

an I1 Call-ID, copied from the I1 Invite message;

an I1 From header, copied from the I1 Invite message, with the callinguser ID being deleted;

an I1 To header, coped from the I1 Invite message, with the called userID being deleted, where a tag is generated and included, for example,tag=i89r; and

an I1 command sequence (CSeq), copied from the I1 Invite message.

Step 204 to step 207: Establish a CS bearer. ICS UE A initiates a CScall by using the PSI DN as a called number; the MSC server or the MGCFin the CS domain performs conversion between CS signaling and SIPsignaling, and generates a SIP Invite message (including the PSI DN),where the SIP Invite message is finally transmitted to the SCC AS. TheSCC AS associates the stored I1 Invite message by using the PSI DN. TheSCC AS sends a final response 200 OK to the MSC server or the MGCF (toindicate that the call is established successfully). The MSC server orthe MGCF returns an ACK to acknowledge that the 200 OK is received. TheMSC server sends a connect message to UE A to indicate that the CS callis established successfully.

Step 208 to step 210: UE A sends an I1 200 OK response through the I1interface to indicate that the IMS session is established successfully.The header field of the I1 200 OK is the same as that of the I1 sessionprogress message. The SCC AS sends a SIP 200 OK to UE B, where the SIP200 OK indicates that UE A already picks up the phone and that the IMSsession is established successfully. The UE B sends a SIP ACK request tothe SCC AS to acknowledge the 200 OK (received).

In addition to the calling and called scenarios, the I1 interfaceinvolves three more scenarios, that is, the fallback (fallback) from Gminterface to I1 interface, switching from Gm interface to I1 interface,and addition of an I1 interface. The foregoing optimization design mayalso be applicable in these three scenarios.

The following describes the optimization design for service control viathe I1 interface in these scenarios of the fallback (fallback) from Gminterface to I1 interface, switching from Gm interface to I1 interface,and addition of an I1 interface.

Embodiment 1: An embodiment of the present invention provides a methodfor service control via the I1 interface in a Gm fallback scenario. Fromthe perspective of an SCC AS, the execution procedure may include that:The SCC AS sends a SIP Invite message to the ICS UE through the Gminterface; if a response message returned by the ICS UE is received,where the response message indicates that the ICS UE chooses to use theCS bearer and use I1 interface for control, an I1 Invite message is sentto the ICS UE through the I1 interface, where the I1 Invite messageincludes information indicating that Gm interface (service) controlfalls back to the I1 interface (service) control and information used toassociate the SIP Invite message. Preferably, the foregoing two piecesof information are included in a replace header field. Optionally, theI1 Invite message uses the Call-ID and tag of a SIP dialog as theCall-ID of the I1 interface and the tag of the I1 interface, where theSIP dialog is triggered and generated by the SIP Invite message. Note:For simplification, the tag of the I1 interface may be omitted.

Analysis: Because the UE may obtain a calling user identifier, a calleduser identifier, and privacy (privacy) through the SIP Invite message,the SCC AS may omit the calling user identifier, called user identifierand privacy when re-delivering a call request (that is, an I1 Invitemessage). In addition, to enable the UE to associate the I1 call requestand the previous SIP Invite message, the SCC AS should includeassociation information, for example, using a replace (replace) headerincluding an SIP dialog (dialog) Call-ID and a tag (the tag isoptionally included), and further using the SIP dialog Call-ID and tagby default as the I1 Call-ID and I1 tag respectively. Therefore, the SCCAS does not need to include a new I1 Call-ID and I1 tag (the includes anI1 From tag and an I1 To tag) in the I1 Invite message. In this way,optimization is achieved in the following two aspects: The calling useridentifier and the called user identifier are omitted (the UE associatesthe stored calling user ID and called user ID by using the SIP dialogCall-ID and the tag), and the operation of generating a new I1 Call-IDand I1 tag is omitted.

In the foregoing embodiment, the SCC AS may send a SIP Invite message toUE A through the Gm interface, where the SDP information in the SIPInvite message includes packet switched media (Packet Switched media, PSmedia) information and circuit switched CS media information. The CSmedia information indicates that UE A may select the CS bearer, and mayalso include a PSI DN. UE A decides to use the CS bearer transmit themedia streams of the session and use the I1 interface for servicecontrol, and returns a SIP session progress (SIP 183) response(indicating that the CS bearer and I1 interface for control are used) tothe SCC AS. The SCC AS delivers a call request to UE A through the I1interface, establishes an IMS session, and releases the SIP dialog.

More specifically, as shown in FIG. 3, the procedure in the Gm fallbackscenario may include the following steps:

Step 301: The SCC AS receives a SIP Invite message that includes acalling user identifier (for example, set to user_b@example.com) and acalled user identifier (for example, set to user_a@example.com).

Step 302: The SCC AS sends an I1 Invite message to the ICS UE A throughthe Gm interface to initiate an IMS session, where the I1 Invite messageincludes the following information (the SCC AS also stores theinformation):

a Call-ID (Call-ID), used to identify this IMS session or call, forexample, set to I93j9xsKKIg374js7u8JY;

a From header (From header), where the value of the header field is usedto indicate the calling user identifier of the IMS session, for example,set to user_b@example.com, where the From header also includes a tag(tag), for example, set to 094P;

a To Header (To Header), used to indicate the called user ID of the IMSsession, for example, set to user_a@example.com;

a command sequence (CSeq, Command Sequence), for example, set to 891Invite; and

SDP (Session Description Protocol, Session Description Protocol)information, including PS media information and CS media information,where the CS media information indicates that the UE A may choose the CSbearer, and may include a PSI DN, for example, set to +12125556886.

Step 303: After receiving the SIP Invite message, ICS UE A stores theCall-ID, From header, To header, and CSeq. UE A decides to use the CSbearer to transmit media streams of the session, and returns a response(the returned response may generate a SIP dialog. The SIP dialog is anattribute of the SIP and used for subsequent SIP message communication)to the SCC AS through the Gm interface, for example, 183 (sessionprogress, session progress), where the response includes the followinginformation:

a Call-ID, copied from the SIP Invite message;

a From header, copied from the SIP Invite message;

a To header, copied from the SIP Invite message and including a tag, forexample, tag=io7p; and

a command sequence (CSeq), copied from the SIP Invite message.

Step 304: The SCC AS sends an I1 Invite message (not including the I1Call-ID header, I1 From header, and I1 To header) to the UE A throughthe I1 interface, where the I1 Invite message includes the followinginformation:

an I1 Replace header, where the header field indicates that the I1Invite replaces the foregoing SIP Invite and includes SIP dialog Call-IDinformation and tag information; and

a command sequence (CSeq, Command Sequence), for example, set to CSeq:891 Invite.

Step 305: ICS UE A receives the I1 Invite message, identifies, throughthe I1 Replace header, the fallback from Gm interface to I1 interface,and finds the stored SIP dialog information (including calling andcalled user identifiers) according to the I1 Replace header information.The UE performs a normal called session (session) establishment process(for the process, reference may be made to the procedure in which an ICSUE is called) via the I1 interface by using the SIP dialog Call-ID andtag as the I1 Call-ID and I1 tag. In addition, the UE or the SCC AS mayinitiate releasing of the SIP dialog via the Gm interface.

Embodiment 2: An embodiment of the present invention provides a methodfor service control in a Gm interface control switching scenario. Fromthe perspective of the SCC AS, the execution procedure may include:receiving an I1 Invite message sent by the IMS centralized services userequipment, where the replace header field of the I1 Invite messageincludes a service control switching request indication and a SessionInitiation Protocol dialog ID; searching for an IMS session through theforegoing Session Initiation Protocol dialog ID; and sending an I1success message to the user equipment to indicate that the I1 interfacefor service control is switched successfully.

Specifically, the I1 interface Call-ID of the I1 Invite message is adialog identifier of the Session Initiation Protocol dialog.

In the foregoing embodiment, two technical problems that need to besolved in service control switching are solved. One is therepresentation of the service control switching request, and the otheris the establishment of an I1 Call-ID and I1 tag. A replace (replace)header (carrying the SIP dialog ID of the Gm interface) is included inthe I1 Invite request to indicate that the service control of the Gminterface is replaced. In addition, the I1 Call-ID and the I1 tag mayreuse the Call-ID and tag of the SIP dialog ID. In this way, the I1Invite message may omit the transfer of the I1 Call-ID header, I1 Fromheader, and I1 To header. After receiving a service control switchingrequest, the SCC AS returns an I1 200 OK to indicate that the servicecontrol is switched successfully. Subsequently, the UE may performservice control through the I1 interface. In this way, optimization isachieved in the following two aspects: The calling and the called useridentifiers are omitted (the SCC AS associates the IMS session, thecalling user ID and the called user ID with the Replace header), and theoperation of generating a new I1 Call-ID and I1 tag is omitted.

More specifically, as shown in FIG. 4, the procedure in a Gm switchingscenario may include the following steps:

Step 401: UE A sends an I1 Invite message (not including an I1 Call-IDheader, an I1 From header, and an I1 To header; consistent with theinformation in the SIP dialog by default) to the SCC AS, where the I1Invite message includes the following information:

a Replace header, where the header field indicates a service controlswitching request and includes a dialog ID of the SIP dialog; and

an I1 command sequence (CSeq, Command Sequence), for example, set toCSeq: 263 Invite.

Step 402: The SCC AS finds the SIP dialog (used to control the IMSsession) through the replace header information, and identifies that theIMS session already use the CS bearer to transmit data streams. The SCCAS sends a I1 200 OK to respond to the UE A to indicate that the servicecontrol is switched successfully. If the IMS session uses the PS domainto transmit media streams, a CS bearer needs to be created. The SIPdialog Call-ID and tag are used as the I1 Call-ID and I1 tagrespectively. Subsequently, the UE may perform service control throughthe I1 interface. The UE or the SCC AS may initiate the releasing of theSIP dialog.

Embodiment 3: An embodiment of the present invention provides a methodfor service control in a scenario where service control via an I1interface is added. From the perspective of the SCC AS, the executionprocedure may include that: The SCC AS receives an I1 Invite messagesent by the IMS centralized services user equipment, where the I1 Invitemessage includes a session transfer identifier (Session TransferIdentifier, STI) indicating that service control via an I1 interface isadded (or an I1 interface is added), where the STI may be used as avalue of a Request uniform resource identifier (Request URI) or the Toheader (To header); the SCC AS obtains the CS domain number (forexample, a Mobile Station ISDN (MSISDN, Mobile Station ISDN) or MDN(Mobile Directory Number, mobile directory number)) of the UE throughthe lower transport layer, and then searches for an Internet Protocolmultimedia subsystem session according to the CS domain number orsearches for an Internet Protocol multimedia subsystem session accordingto the foregoing STI; the SCC AS sends an I1 Invite success message tothe user equipment to indicate that the I1 interface is addedsuccessfully.

The execution scenario of the foregoing procedure may be as follows: TheUE A decides to add an I1 interface in order to hold a current IMSsession and establish a second session. In this case, the foregoing I1Invite message further includes indication information indicating thatthe current Internet Protocol multimedia subsystem session is held.

Alternatively, the SCC AS may deliver a new IMS session (according tothe normal called procedure) through the I1 interface, while UE A needsto hold the first session and connect the second session (a new IMSsession). In this case, before the step of receiving an I1 Invitemessage sent by the IMS centralized services user equipment, theexecution procedure further includes: The SCC AS sends an I1 Invitemessage to the user equipment, and initiates a new Internet Protocolmultimedia subsystem session.

Alternatively, the SCC AS may initiate the addition of service controlvia an I1 interface. The SCC AS makes service control via the I1interface added through the I1 invite message (not carrying calling andcalled user identifier). The specific scenario may be as follows: A peerend adds or deletes a video or has other information that needs to besent to the UE. In this case, from the perspective of the ICS UE, theexecution procedure may include:

receiving an I1 Invite message sent by the service centralization andcontinuity application server, where the I1 Invite message includes asession transfer identifier (session transfer identifier, STI)indicating that service control via the I1 interface is added (or an I1interface is added), where the STI may be used as a value of the Requestuniform resource identifier (Request URI) or the To header (To header).

After the SCC AS initiates the addition of service control via the I1interface, the SCC AS may send an I1 Invite message (not includingcalling and called user identifiers) to the UE, where the messageincludes an STI for indicating the UE that the service control via theI1 interface is added. The creation of an I1 Call-ID and an I1 tag mayadopt a manner in the normal I1 interface called process. The current UEhas only one IMS session by default. Therefore, the UE may associate theIMS session.

In the above technical solution, the following three technical issuesare solved in a case where service control via the I1 interface is addedto UE A: one is representation of a request for adding service controlvia the I1 interface, another is establishment of an I1 Call-ID and anI1 tag, and yet another is how the SCC AS associates the IMS session. AnSTI (session transfer identifier, used to perform access transfer in theprior art, for example, used to transfer media streams from the CSdomain to the PS domain) may be included in the I1 Invite message toindicate a request for adding service control via the I1 interface. Thecreation of an I1 Call-ID and an I1 tag may adopt a manner in the normalI1 interface calling process. The SCC AS may associate the IMS sessionby using the STI (if the STI can uniquely identify UE A) or by using theCS domain UE number (for example, an MSISDN or MDN (Mobile DirectoryNumber)) reported by the SCC AS through the lower transport layer. Inthis way, the optimization is achieved in the following two aspects: Thecalling and called user identifiers are omitted (The SCC AS searches forthe IMS session, the calling and called user identifiers by using theSTI or the CS domain UE number).

More specifically, as shown in FIG. 5, the procedure of the UE addingservice control via the I1 interface may include the following steps:

Step 501: UE A sends an I1 Invite message to the SCC AS, where the I1Invite message includes the following information:

an STI (used as a value of the request (Request) uniform resourceidentifier (Uniform Resource Identifier, URI) header or the To header),indicating that service control via an I1 interface is added;

an I1 Call-ID header and a From tag; and

an I1 command sequence (CSeq, Command Sequence), for example, set toCSeq: 163 Invite.

UE A may include a request for holding the current IMS session, forexample, setting a=inactive (inactive).

Step 502: The SCC AS obtains a CS domain number (for example, the MSISDNand the MDN) of UE A through the lower transport layer, and then findsthe IMS session through the CS domain number or finds the IMS sessionthrough the STI. Then, the SCC AS uses an I1 200 OK (including a To tag)as a response to UE A to indicate that the I1 interface is addedsuccessfully.

Embodiment 4: As shown in FIG. 6, an embodiment of the present inventionprovides a service centralization and continuity application server,including:

a Session Initiation Protocol Invite message sending unit 601,configured to send a Session Initiation Protocol Invite message to auser equipment through a Gm interface;

a response message receiving unit 602, configured to receive a responsemessage returned by the user equipment, where the response messageindicates that the user equipment chooses to use a circuit switchedbearer and use an I1 interface for control; and

an I1 Invite message sending unit 603, configured to send an I1 Invitemessage to the user equipment through the I1 interface if the responsemessage receiving unit 602 receives the response message, where the I1Invite message carries information indicating that Gm interface controlfalls back to the I1 interface control and information used to associatethe Session Initiation Protocol Invite message.

Further, as shown in FIG. 7, the foregoing service centralization andcontinuity application server includes:

an identifier setting unit 701, configured to set the I1 interfaceCall-ID of the I1 Invite message to a Call-ID of a dialog of the SessionInitiation Protocol Invite message.

In the foregoing embodiment, the replace header of the I1 Invite messageis used to carry information indicating that Gm interface control fallsback to the I1 interface control and information used to associate theSession Initiation Protocol Invite message, which omits the calling andcalled user identifiers. In addition, the Call-ID of a dialog of theforegoing Session Initiation Protocol Invite message is used as the I1interface Call-ID, so the I1 dialog ID may be omitted. Therefore, theoverheads of the I1 protocol message are reduced.

Embodiment 5: As shown in FIG. 8, an embodiment of the present inventionprovides a service centralization and continuity application server,including:

an I1 Invite message receiving unit 801, configured to receive an I1Invite message sent by a user equipment, where the I1 Invite messagecarries a service control switching request indication and a dialogidentifier of a Session Initiation Protocol session;

a session searching unit 802, configured to search for a SessionInitiation Protocol session by using the dialog identifier of theSession Initiation Protocol session; and

a switching success message sending unit 803, configured to send amessage, which indicates that service control is switched successfully,to the UE.

Optionally, the I1 interface Call-ID of the I1 Invite message receivedby the I1 Invite receiving unit 801 is the Call-ID of the SessionInitiation Protocol dialog.

In the foregoing embodiment, the I1 Invite message carries the servicecontrol switching request indication and the session identifier of theSession Initiation Protocol session, so the calling and called useridentifiers may be omitted. In addition, the Call-ID of a dialog of theSession Initiation Protocol Invite message is used as the I1 interfaceCall-ID, so the I1 dialog ID may be omitted. Therefore, the overheads ofthe I1 protocol message are reduced.

Embodiment 6: As shown in FIG. 9, an embodiment of the present inventionprovides a service centralization and continuity application server,including:

an I1 Invite message receiving unit 901, configured to: receive an I1Invite message sent by a user equipment, where the I1 Invite messagecarries an indication indicating that an I1 interface is added in theIMS session; and the indication indicating that an I1 interface is addedin the Internet Protocol multimedia subsystem session is carried bysetting a value of a Request uniform resource identifier or a To headerof the I1 Invite message to a session transfer identifier, or carried bya public service identity directory number included in the I1 Invitemessage, where the public service identity directory number is thenumber of the other party of the IMS session;

a session searching unit 902, configured to search for the InternetProtocol multimedia subsystem session by using the session transferidentifier or the public service identity directory number; or a sessionsearching unit 902, configured to obtain a circuit switched domainnumber of the user equipment through the lower transport layer, and thensearch for the Internet Protocol multimedia subsystem session by usingthe circuit switch domain number; and a request success message sendingunit 903, configured to send a message, which indicates that the I1interface is added successfully, to UE.

In the foregoing embodiment, an I1 Invite message is used to carry anindication indicating that an I1 interface is added in the IMS session,so the calling and called user identifiers are omitted. Therefore, theoverheads of the I1 protocol message are reduced.

Embodiment 7: As shown in FIG. 10, a seventh embodiment of the presentinvention provides a user equipment, including:

an I1 Invite message receiving unit 1001, configured to receive an I1Invite message sent by the service centralization and continuityapplication server, where the I1 Invite message carries informationindicating that service control via an I1 interface is added in the IMSsession; and

an I1 interface service control establishing unit 1002, configured to:establish the service control via an I1 interface, and associate theservice control via the I1 interface with the IMS session.

In the foregoing embodiment, an I1 Invite message is used to carry anindication indicating that an I1 interface is added in the IMS session,so the calling and called user identifiers are omitted. Therefore, theoverheads of the I1 protocol message are reduced.

Embodiment 8: As shown in FIG. 11, an embodiment of the presentinvention further provides a system for service control via the I1interface, including:

an service centralization and continuity application server 1101,configured to: send a Session Initiation Protocol Invite message to auser equipment 1102 through the Gm interface; if receiving a responsemessage returned by a user equipment 1102, where the response messageindicates that the user equipment chooses to use a circuit switch bearerand an I1 interface for control, send an I1 Invite message to the userequipment 1102 through the I1 interface, where the I1 Invite messagecarries information indicating that Gm interface control falls back tothe I1 interface control and information used to associate the SessionInitiation Protocol Invite message; and

the user equipment 1102, configured to: after receiving a SessionInitiation Protocol Invite message, send a response message to theservice centralization and continuity application server, where theresponse message indicates that the user equipment 1102 chooses thecircuit switched bearer and I1 interface for control; receive an I1Invite message, and parse the I1 Invite message to obtain informationindicating that Gm interface control falls back to the I1 interfacecontrol and information used to associate the Session InitiationProtocol Invite message.

Optionally, the I1 interface Call-ID of the I1 Invite message sent bythe service centralization and continuity application server 1101 is theCall-ID of a dialog of the SIP Invite message.

The user equipment 1102 is further configured to perform a calledsession establishment process via the I1 interface by using the SessionInitiation Protocol Invite message to generate the Call-ID of the dialogas the I1 interface Call-ID.

In the foregoing embodiment, the I1 Invite message is used to carryinformation indicating that Gm interface control falls back to the I1interface control and information used to associate the SessionInitiation Protocol Invite message, so the calling and called useridentifiers may be omitted. In addition, the Call-ID of the dialog ofthe foregoing Session Initiation Protocol Invite message is used as theI1 interface Call-ID, so the I1 dialog ID may be omitted. Therefore, theoverheads of the I1 protocol message are reduced.

Embodiment 9: As shown in FIG. 12, an embodiment of the presentinvention provides a system for service control via an I1 interface,including:

an service centralization and continuity application server 1201,configured to: receive an I1 Invite message sent by a user equipment1202, where the I1 Invite message carries a service control switchingrequest indication and a Call-ID of the Session Initiation Protocoldialog; search for an Internet Protocol multimedia subsystem sessionthrough the Call-ID of the Session Initiation Protocol dialog; and senda message, which indicates that service control is switchedsuccessfully, to the user equipment 1202; and

the user equipment 1202, configured to: send an I1 Invite message to theservice centralization and continuity application server 1201; andreceive the I1 success message to know that service control is switchedsuccessfully.

Optionally, the I1 interface Call-ID of the I1 Invite message sent bythe user equipment 1202 is the Call-ID of the Session InitiationProtocol dialog.

Receiving, by the service centralization and continuity applicationserver 1201, the I1 Invite message sent by the user equipment includes:receiving an I1 Invite message sent by the user equipment, where the I1interface Call-ID in the I1 Invite message is the session identifier ofthe Session Initiation Protocol session, and performing a callingsession establishment process via the I1 interface.

In the foregoing embodiment, an I1 Invite message is used to carry aservice control switching request and a session identifier of theSession Initiation Protocol session, so the calling and called useridentifiers may be omitted. In addition, the Call-ID of the dialog ofthe Session Initiation Protocol Invite message is used as the I1interface Call-ID, so the I1 dialog ID may be omitted. Therefore, theoverheads of the I1 protocol message are reduced.

Embodiment 10: As shown in FIG. 13, an embodiment of the presentinvention provides a system for service control via the I1 interface,including:

an service centralization and continuity application server 1301,configured to: receive an I1 Invite message sent by a user equipment1302, where the I1 Invite message carries an indication indicating thatan I1 interface is added in an Internet Protocol multimedia subsystemsession, where the indication is carried by setting the value of theRequest uniform resource identifier or the To header of the I1 Invitemessage to a session transfer identifier or carried by a public serviceidentity directory number included in the I1 Invite message, and thepublic service identity directory number is the number of the otherparty of the Internet Protocol multimedia subsystem session; search forthe Internet Protocol multimedia subsystem session through the sessiontransfer identifier or the public service identity directory number, orobtain a circuit switched domain number of the user equipment 1302through the lower transport layer and search for the Internet Protocolmultimedia subsystem session by using the circuit switched domainnumber; and send a message, which indicates that the I1 interface isadded successfully, to the user equipment 1302; and

the user equipment 1302, configured to: send an I1 Invite message to theservice centralization and continuity application server 1301; andreceive an I1 success message to know that the I1 interface is addedsuccessfully.

In the foregoing embodiment, an I1 Invite message is used to carry anindication indicating that an I1 interface is added to the IMS session,so the calling and called user identifiers may be omitted. Therefore,the overheads of the I1 protocol message are reduced.

Embodiment 11: As shown in FIG. 14, an embodiment of the presentinvention provides a system for service control via the I1 interface,including:

a user equipment 1402, configured to: receive an I1 Invite message sentby an service centralization and continuity application server 1401,where the I1 Invite message indicates that service control via an I1interface is added in an IMS session, and establish service control viaan I1 interface to associate the service control via an I1 interfacewith the IMS session; and

the service centralization and continuity application server 1401,configured to send an I1 Invite message to the user equipment 1402,where the I1 Invite message indicates that service control via an I1interface is added in the IMS session.

In the foregoing embodiment, an I1 Invite message is used to carry anindication indicating that an I1 interface is added in an IMS session,so the calling and called user identifier may be omitted. Therefore, theoverheads of the I1 protocol message are reduced.

Embodiment 12: As shown in FIG. 15, an embodiment of the presentinvention provides a user equipment, including:

an Invite message receiving unit 1501, configured to: receive a SessionInitiation Protocol Invite message sent by a service centralization andcontinuity application server through the Gm interface, where theSession Initiation Protocol Invite message carries a response messageindicating that a circuit switch bearer and an I1 interface for controlare used;

a response message sending unit 1502, configured to: after receiving theSession Initiation Protocol Invite message, send the response messagecarrying an indication indicating that a circuit switched bearer and anI1 interface for control are used;

an I1 Invite message receiving unit 1503, configured to receive an I1Invite message via the I1 interface; and

an I1 Invite message parsing unit 1504, configured to: parse the I1Invite message, and obtain information indicating that Gm interfacecontrol falls back to the I1 interface control and information used toassociate the Session Initiation Protocol Invite message.

Further, as shown in FIG. 16, the I1 interface Call-ID of the I1 Invitemessage is a Call-ID of a dialog generated by the Session InitiationProtocol Invite message. The user equipment further includes:

a session establishing unit 1601, configured to perform a called sessionestablishment process via the I1 interface by using the Call-ID of thedialog of the Session Initiation Protocol Invite message as the I1interface Call-ID.

Embodiment 13: As shown in FIG. 17, an embodiment of the presentinvention provides a user equipment, including:

an I1 Invite message sending unit 1701, configured to send an I1 Invitemessage to a service centralization and continuity application server,where the I1 Invite message carries a service control switching requestindication and a Session Initiation Protocol dialog identifier of anInternet Protocol multimedia subsystem session; and

a switching success message receiving unit 1702, configured to receive amessage indicating that service control is switched successfully.

Further, as shown in FIG. 18, the foregoing I1 request sending unit 1601includes:

an identifier setting unit 1801, configured to set the I1 interfaceCall-ID of the I1 Invite message to a Call-ID of the Session InitiationProtocol dialog.

The foregoing user equipments and the service centralization andcontinuity application servers may be used for service control via theI1 interface.

It can be understood by persons of ordinary skill in the art that all orpart of the steps in the methods in the embodiments may be performed bya program instructing hardware. The program may be stored in a computerreadable storage medium, such as a Read Only Memory, a magnetic disk,and an optical disk.

Detailed above are a method, an apparatus, and a system for servicecontrol via the I1 interface according to the embodiments of the presentinvention. Although the principle and implementation of the presentinvention are described with reference to specific examples in thisdocument, the embodiments are only intended to help understand themethod and core idea of the present invention. In addition, with respectto the specific implementation and application scope, modifications andvariations may be made by persons of ordinary skill in the art accordingto the idea of the present invention. Therefore, the content of thespecification shall not be construed as a limitation on the presentinvention.

1. A method for service control via an I1 interface, the methodcomprising: sending a Session Initiation Protocol Invite message to auser equipment through a Gm interface; receiving a response messagereturned by the user equipment, wherein the response message indicatesthat the user equipment chooses to use a circuit switched bearer and usean I1 interface for control; sending an I1 Invite message to the userequipment through the I1 interface, wherein the I1 Invite messagecarries information indicating that Gm interface control falls back tothe I1 interface control and information used to associate the SessionInitiation Protocol Invite message.
 2. The method according to claim 1,wherein the information indicating that Gm interface control falls backto the I1 interface control and the information used to associate theSession Initiation Protocol Invite message is carried by a replaceheader field of the I1 Invite message.
 3. The method according to claim1, wherein an I1 interface Call-ID of the I1 Invite message is a Call-IDof a dialog generated by the Session Initiation Protocol Invite message.4. A method for service control via an I1 interface, the methodcomprising: receiving an I1 Invite message sent by a user equipment,wherein the I1 Invite message carries a service control switchingrequest indication and a Session Initiation Protocol dialog identifierof an Internet Protocol multimedia subsystem session; searching for theInternet Protocol multimedia subsystem session through the SessionInitiation Protocol dialog identifier; and sending a message to the userequipment, the message indicating that service control is switchedsuccessfully.
 5. The method according to claim 4, wherein the servicecontrol switching request indication of the Internet Protocol multimediasubsystem session and the Session Initiation Protocol dialog identifierare carried by a replace header field of the I1 Invite message.
 6. Themethod according to claim 4, wherein an I1 interface Call-ID of the I1Invite message is a Call-ID of the Session Initiation Protocol dialog.7. A service centralization and continuity application server, theserver comprising: a Session Initiation Protocol Invite message sendingunit, configured to send a Session Initiation Protocol Invite message toa user equipment through a Gm interface; a response message receivingunit, configured to receive a response message returned by the userequipment, wherein the response message indicates that the userequipment chooses to use a circuit switched bearer and use an I1interface for service control; and an I1 Invite message sending unit,configured to send an I1 Invite message to the user equipment throughthe I1 interface if the response message receiving unit receives theresponse message, wherein the I1 Invite message carries informationindicating that Gm interface control falls back to the I1 interfacecontrol and information used to associate the Session InitiationProtocol Invite message.
 8. The service centralization and continuityapplication server according to claim 7, further comprising anidentifier setting unit, configured to set an I1 interface Call-ID ofthe I1 Invite message to a Call-ID of a dialog generated by the SessionInitiation Protocol Invite message.
 9. A service centralization andcontinuity application server, the server comprising: an I1 Invitemessage receiving unit, configured to receive an I1 Invite message sentby a user equipment, wherein the I1 Invite message carries a servicecontrol switching request indication and a Session Initiation Protocoldialog identifier of an Internet Protocol multimedia subsystem session;a session searching unit, configured to search for the Internet Protocolmultimedia subsystem session through the Session Initiation Protocoldialog identifier; and a switching success message sending unit,configured to send a message, which indicates that service control isswitched successfully, to the user equipment.
 10. A user equipment,comprising: an Invite message receiving unit, configured to receive aSession Initiation Protocol Invite message sent by a servicecentralization and continuity application server through a Gm interface;a response message sending unit, configured to send a response messageafter receiving the Session Initiation Protocol Invite message, whereinthe response message indicates that the user equipment chooses to use acircuit switched bearer and use an I1 interface for control; an I1Invite message receiving unit, configured to receive an I1 Invitemessage through the I1 interface; and an I1 Invite message parsing unit,configured to parse the I1 Invite message to obtain informationindicating that Gm interface control falls back to the I1 interfacecontrol and information used to associate the Session InitiationProtocol Invite message.
 11. The user equipment according to claim 10,wherein an I1 interface Call-ID of the I1 Invite message is a Call-ID ofa dialog generated by the Session Initiation Protocol Invite message,the user equipment further comprising: a session establishing unit,configured to perform a called session establishment process via the I1interface by using the Call-ID of the dialog of the Session InitiationProtocol Invite message as the I1 interface Call-ID.
 12. A userequipment, comprising: an I1 Invite message sending unit, configured tosend an I1 Invite message to a service centralization and continuityapplication server, wherein the I1 Invite message carries a servicecontrol switching request indication and a Session Initiation Protocoldialog identifier of an Internet Protocol multimedia subsystem session;and a switching success message receiving unit, configured to receive amessage indicating that service control is switched successfully. 13.The user equipment according to claim 12, wherein the I1 Invite messagesending unit comprises an identifier setting unit, configured to set anI1 interface Call-ID of the I1 Invite message to a Call-ID of theSession Initiation Protocol dialog.